The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
Traditional automatic transmissions use friction clutches in the form of either band clutches or multi-plate friction clutches. Friction clutches work by pressing two plates together. Friction between clutch elements allows the transfer of energy by allowing one plate to spin faster than the other or to slip. Automatic transmissions use friction clutches so that changing gear doesn't require engine power to drop. While changing gears, an automatic transmission can disconnect one clutch as it engages another. When ambient temperature drops below zero, however, and particularly at temperatures approaching −40° F. the hydraulic fluid pressure required to actuate friction clutches requires increased pump capacity, which may not be available in smaller engine and vehicle designs.
Dog clutches can be used in place of friction clutches and are commonly used in manual transmissions. Dog clutches are interference in lieu of slip clutches. Power is transmitted by a tooth of one side pressing on a tooth of the other side. Dog clutches cannot slip therefore they are either engaged or disengaged. Dog clutches suffer little parasitic loss and are simple and compact. Synchronizer dog clutches commonly employed in manual transmissions synchronize the speed of two components prior to engagement of those two components. Known synchronizers include a conical sleeve integrally connected to a blocker or dog ring. The sleeve has a set of teeth and is rotationally fixed to a first component and is longitudinally translatable along an axis of rotation to engage a set of teeth located on a second component. Longitudinal movement of the sleeve toward the direction of the second component initially causes a frusto-conical surface of the blocker ring to engage a matching frusto-conical surface on the second component prior to engagement of the teeth. Engagement of these two surfaces is a clutching action which causes the second component to be speed synchronized with the blocker ring and sleeve and thus the first component.
Known dog clutch synchronizers and their conical sleeves and one-way ball bearing clutches are limited in that they only provide actuator force in one direction. In an application such as engagement of a final drive planetary gear set with a differential, known dog clutches do not allow actuation under load.